- dead reckoning (n.)
[dead reckoning 词源字典]
- "ascertaining the position of a ship by measurement of the distance run," 1610s, might be from nautical abbreviation ded. ("deduced") in log books, but it also fits dead (adj.) in the sense of "unrelieved, absolute."[dead reckoning etymology, dead reckoning origin, 英语词源]